Insider holdings that are under some other kind of sales restriction. Restricted stock must be traded in compliance with special SEC regulations.
Investopedia Says:
Insiders are given restricted stock after merger and acquisition activity, underwriting activity, and affiliate ownership in order to prevent premature selling that might adversely affect the company. Restricted stock cannot be sold without registration with the SEC (under the Securities Act of 1933)or some other special exemption.
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